The present invention relates to a light quantity adjusting device, which is assembled in a photographing device such as a digital camera and a mobile telephone with a camera for adjusting quantity of photographic light through a shutter blade or iris blades, and relates to a photographic device having the light quantity adjusting device.
Generally, in a light quantity adjusting device, a base plate (or a main plate) having an aperture is arranged in a photographic optical path leading from an object to an image lens, and a shutter blade(s) and iris blades are individually rotatably or slidably supported on the base plate and are opened/closed by individual drive motors attached to the base plate.
In a light quantity adjusting device disclosed in Patent Publication 1 (Japanese Patent Publication (Kokai) No. 10-221740), a shutter blade and iris blades are rotatably supported at their base end portions through pins on a base plate having an optical aperture at its center, so that their leading ends face the optical pass aperture. In the light quantity adjusting device in Patent Publication 1, the shutter blade is formed of two blade members to be turned in the opposite directions from each other, and the iris blades are arranged such that a blade member for closing the aperture to a large area and a blade member for closing the aperture to a small area are arranged to face the aperture selectively.
As shown in FIG. 8, there is disclosed a structure, in which a shutter drive unit (or a moving magnet) X4 for opening/closing a pair of shutter blades X3; a first iris drive unit (or a moving magnet) X6 for moving a first iris blade X5 having a smaller aperture than an exposure aperture X2 formed at the center of a main plate X1 suitably to and from the exposure aperture X2; and a second iris drive unit (or a moving magnet) X8 for moving a second iris blade X7 having a far smaller aperture than the exposure aperture X2 suitably to and from the exposure aperture X2 are arranged at a substantially equal spacing around the exposure aperture X2.
The light quantity adjusting device is formed to arrange the plural common drive units X4, X6 and X8 at the common distance around the exposure aperture X2 of the main plate X1. Accordingly, it is necessary to provide a space matching to a diameter of the drive units around the exposure aperture X2. Due to the arrangement of the drive units X4, X6 and X8 at the circumferential edge of the aperture of the main plate, it is difficult to keep the arranging spaces for the drive units X4, X6 and X8 in a case of a lens barrel which moves back and force like a zoom lens. At an especially high shutter speed, the drive unit X4 for opening/closing the shutter blade X3 has to be formed as a unit having a high output torque, thereby increasing a size of the device large.
In Patent Publication 2 (Japanese Patent Publication (Kokai) No. 2002-049076), a shutter device is disclosed as a drive device for opening/closing a pair of shutter blades Y2 and Y3, which are arranged between a holder plate Y1 and a main plate Y4, as shown in FIG. 9. The shutter device includes: a generally cylindrical magnet rotor Y5 having a drive arm protruding from a side portion and magnetically divided into N and S poles; an auxiliary stator Y6 inserted into a hollow portion of the rotor Y5; a stator Y8 made of a soft magnetic material and having a column-shaped inner cylinder for fitting the auxiliary stator Y6 therein and an outer magnetic pole 3a having a tooth-shaped leading end portion; and a conduction coil Y7.
The stator Y8 and the auxiliary stator Y6 are magnetized by the conduction coil Y7 thereby to drive the intervening magnet rotor Y5 magnetically rotationally. Therefore, the shutter device has a higher magnetic efficiency than that of the structure in Patent Publication 1, and has a merit that the drive device can be small-sized for the higher magnetic efficiency.
In Patent Publication 3 (Japanese Patent Publication (Kokai) No. 2002-272082), there is disclosed a structure, in which there are arranged sequentially in the direction of an optical axis a blade holder Z1, blades Z2, a main plate Z3, a magnet rotor Z4 having a hollow cylinder shape, a magnet holder Z5, a cylindrical coil Z6, and a stator Z7 having an outer cylinder having a leading end portion extending in the axial direction and formed into a plurality of comb teeth. The light quantity adjusting device is ring-shaped to pass an optical path through the central portion of the drive device, so that it can be easily built in the cylindrical lens barrel of a zoom lens.
As a size of the device has been reduced as in a recent mobile telephone having a built-in camera, the light quantity adjusting device has a small base plate and small blades to be assembled into the base plate. The small-sized drive device has a low output torque, thereby making it difficult to drive the blades at a high speed. Therefore, the structure in Patent Publication 1 has a limit in the size reduction, and the structure in Patent Publication 3 can make the device small and flattened.
In the Patent Publications, the blade is structured by the shutter blade or the iris blade. Accordingly, when both the shutter blade and the iris blade are assembled in a common base plate and driven by an individual drive motor, in the structure in Patent Publication 3, it is necessary to arrange two ring-shaped magnets around the optical path aperture. Further, in Patent Publication 3, the N/S magnetic poles are alternately arranged on the circumferential side of the ring-shaped magnet rotors and the yokes of the inducing iron members are arranged to face on the rotor circumferential sides. Accordingly, it is difficult to magnetically shield the magnetic field generated in the coil, and the magnetic fields of the magnets and the inducing iron members may exert magnetic influences therearound.
In view of the problems described above, an object of the present invention is to provide a small-sized compact light quantity adjusting device, in which shutter blades for shutting the photographing light quantity, an iris blade for adjusting the light quantity, and a drive device for opening/closing the blades are assembled in a common base plate.
Another object of the invention is to provide a light quantity adjusting device, in which blade members are prevented from any operation irregularity due to mutual interference among the magnetic fields of magnets, coils, and the like, when a plurality of drive units is assembled in a base plate, and a photographing device using the light quantity adjusting device.
Further objects and advantages of the invention will be apparent from the following description of the invention.